Dr Heather Loenser, a New Jersey vet, said: "Where is there a single shred of documented evidence that marijuana does cats or dogs good?

"I have seen the results of pets that have either been fed pot or have got into a stash or bong themselves. It's horribly cruel and the animals are clearly in distress. I have heard of quite a few deaths."

Dr Tina Wismer, director of the Animal Poison Control Centre, said: "Blood pressure can soar and, without treatment, some animals can go into comas and die."